cmd/tailscaled: make the outbound HTTP/SOCKS5 proxy modular

Updates #12614

Change-Id: Icba6f1c0838dce6ee13aa2dc662fb551813262e4
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/tailscaled/proxy.go

@@ -1,7 +1,7 @@
 // Copyright (c) Tailscale Inc & AUTHORS
 // SPDX-License-Identifier: BSD-3-Clause
 
-//go:build go1.19
+//go:build !ts_omit_outboundproxy
 
 // HTTP proxy code
 
@@ -9,13 +9,105 @@ package main
 
 import (
 	"context"
+	"flag"
 	"io"
+	"log"
 	"net"
 	"net/http"
 	"net/http/httputil"
 	"strings"
+
+	"tailscale.com/net/proxymux"
+	"tailscale.com/net/socks5"
+	"tailscale.com/net/tsdial"
+	"tailscale.com/net/tshttpproxy"
+	"tailscale.com/types/logger"
 )
 
+func init() {
+	hookRegisterOutboundProxyFlags.Set(registerOutboundProxyFlags)
+	hookOutboundProxyListen.Set(outboundProxyListen)
+}
+
+func registerOutboundProxyFlags() {
+	flag.StringVar(&args.socksAddr, "socks5-server", "", `optional [ip]:port to run a SOCK5 server (e.g. "localhost:1080")`)
+	flag.StringVar(&args.httpProxyAddr, "outbound-http-proxy-listen", "", `optional [ip]:port to run an outbound HTTP proxy (e.g. "localhost:8080")`)
+}
+
+// outboundProxyListen creates listeners for local SOCKS and HTTP proxies, if
+// the respective addresses are not empty. args.socksAddr and args.httpProxyAddr
+// can be the same, in which case the SOCKS5 Listener will receive connections
+// that look like they're speaking SOCKS and httpListener will receive
+// everything else.
+//
+// socksListener and httpListener can be nil, if their respective addrs are
+// empty.
+//
+// The returned func closes over those two (possibly nil) listeners and
+// starts the respective servers on the listener when called.
+func outboundProxyListen() proxyStartFunc {
+	socksAddr, httpAddr := args.socksAddr, args.httpProxyAddr
+
+	if socksAddr == httpAddr && socksAddr != "" && !strings.HasSuffix(socksAddr, ":0") {
+		ln, err := net.Listen("tcp", socksAddr)
+		if err != nil {
+			log.Fatalf("proxy listener: %v", err)
+		}
+		return mkProxyStartFunc(proxymux.SplitSOCKSAndHTTP(ln))
+	}
+
+	var socksListener, httpListener net.Listener
+	var err error
+	if socksAddr != "" {
+		socksListener, err = net.Listen("tcp", socksAddr)
+		if err != nil {
+			log.Fatalf("SOCKS5 listener: %v", err)
+		}
+		if strings.HasSuffix(socksAddr, ":0") {
+			// Log kernel-selected port number so integration tests
+			// can find it portably.
+			log.Printf("SOCKS5 listening on %v", socksListener.Addr())
+		}
+	}
+	if httpAddr != "" {
+		httpListener, err = net.Listen("tcp", httpAddr)
+		if err != nil {
+			log.Fatalf("HTTP proxy listener: %v", err)
+		}
+		if strings.HasSuffix(httpAddr, ":0") {
+			// Log kernel-selected port number so integration tests
+			// can find it portably.
+			log.Printf("HTTP proxy listening on %v", httpListener.Addr())
+		}
+	}
+
+	return mkProxyStartFunc(socksListener, httpListener)
+}
+
+func mkProxyStartFunc(socksListener, httpListener net.Listener) proxyStartFunc {
+	return func(logf logger.Logf, dialer *tsdial.Dialer) {
+		var addrs []string
+		if httpListener != nil {
+			hs := &http.Server{Handler: httpProxyHandler(dialer.UserDial)}
+			go func() {
+				log.Fatalf("HTTP proxy exited: %v", hs.Serve(httpListener))
+			}()
+			addrs = append(addrs, httpListener.Addr().String())
+		}
+		if socksListener != nil {
+			ss := &socks5.Server{
+				Logf:   logger.WithPrefix(logf, "socks5: "),
+				Dialer: dialer.UserDial,
+			}
+			go func() {
+				log.Fatalf("SOCKS5 server exited: %v", ss.Serve(socksListener))
+			}()
+			addrs = append(addrs, socksListener.Addr().String())
+		}
+		tshttpproxy.SetSelfProxy(addrs...)
+	}
+}
+
 // httpProxyHandler returns an HTTP proxy http.Handler using the
 // provided backend dialer.
 func httpProxyHandler(dialer func(ctx context.Context, netw, addr string) (net.Conn, error)) http.Handler {